1. Field of the Invention
This invention relates to heat exchangers of the thin formed plate-and-fin type and, more particularly, to particular arrangements for joining the manifold sections of such heat exchanger cores to external ducting without undue loading on the core manifold structure.
2. Description of the Prior Art
The use of opposed piping members joined by bellows to a central pressurized member with the entire combination being structurally held together by tie rods between the opposed piping members is known in the prior art. The use of one or more bellows elements to accommodate structural displacement, as by thermal growth or pressure expansion, is also well known in the prior art, as exemplified by the disclosures of U.S. Pat. Nos. 2,787,124, 3,527,291, 1,882,085, 3,916,871, among others. A particular type of externally pressurized bellows is disclosed in the Greek U.S. Pat. 3,850,231. The aforementioned Neary et al U.S. Pat. No. 3,527,291 also discloses the inclusion of restraining rods in the form of U-bolts for limiting the axial expansion of the bellows element thereof. These disclosures are limited to the use of bellows couplings for axial expansion and are not intended or used for accommodating multi-dimensional variation or balancing of applied pressure loads in the manner of the present invention.
The German Pat. No. 667,144 appears to show various combinations of a bellows juncture member between opposed piping with a spring retaining structure for opposing axial expansion of the bellows and possibly non-axial bending or twisting of the bellows.
Externally pressurized bellows provide certain advantages over the more common and better known internally pressurized bellows for use in an expansion joint between piping or the like. The internally pressurized bellows exhibits a tendency to "squirm" as the internal pressure is increased or as bellows "stiffness" is reduced. Long before the bursting pressure of the bellows is reached, the bellows will tend to twist and buckle out of shape. Such bellows elements are limited to uses below the "squirm" pressure. The longer the bellows, the lower the squirm pressure, thus placing inherent limitations on the use of such members.
Where the expansion joint includes a housing communicating with the internal pressure but entirely surrounding the bellow, the tendency to squirm is eliminated. Such externally pressurized bellows are also known in the prior art and are commercially available.